1. Field of the Invention
This invention relates to a power-driven conveyor system having at least one horizontally oriented section for accumulating items moving between a source and a destination.
2. Description of the Prior Art
Many power-driven conveyor systems for accumulating items have sections oriented vertically because they take up less floor space and may be built quite high. However, these systems, which usually use an endless chain and a plurality of pulley wheels, must necessarily have the pulley wheels spaced quite a relative distance apart in order to make room for assemblies which are attached to the endless chain for carrying items thereon. Such exemplary prior art systems are the vertical accumulators covered by U.S. Pat. No. 4,168,776, issued to Hoeboer in 1979; U.S. Pat. No. 4,142,626, issued to Bradley in 1979; and U.S. Pat. No. 2,933,176, issued to Mansson in 1960.
Such vertical accumulators must be run relatively slow because their operation requires reliable transfer of items to be accumulated both into and out of the unit. This relatively slow operational speed is a definite disadvantage.
Another disadvantage of such vertical accumulators is that the assemblies for carrying items to be accumulated are usually a free pivoting design which increases the potential for damage or breakage of fragile items that are being transported or accumulated. Additional disadvantages of such vertical accumulators are that transfer of items into such units usually requires mechanical movement of the items to be accumulated which increases the breakage potential of fragile items. In addition, this mechanical movement of items is generally recognized as being a potential cause of lower production efficiencies because of problems historically associated with these mechanical movements. Also, the assemblies for carrying items to be accumulated do not usually accommodate irregular shapes and sizes because of their inability to reliably transfer and contain such items.
Because of the presence of such carrier assemblies, it has also been a problem to condense the arrangement of the endless chain and the plurality of pulley wheels into a volume occupying significantly less floor space.
There are horizontal accumulators known in the prior art. Exemplary systems are shown in U.S. Pat. No. 3,506,105, issued to Stauber in 1970, U.S. Pat. No. 3,448,846, issued to Bardenhagen in 1969, U.S. Pat. No. 3,370,693, issued to Marsden in 1968; and U.S. Pat. No. 2,932,376, issued to Millington in 1960. However, many prior art horizontal accumulators operate on the LIFO principle, i.e., upon a malfunction of either upstream or downstream equipment, the items are stored in the accumulator in such a manner that the last item into the system is the first item out of the system when the malfunction in the equipment is corrected and the upstream or downstream equipment is up and running again. This LIFO principle of operation is a disadvantage in systems where maintaining sequence of manufacture is important. This LIFO principle of operation also affects reliability in that accumulated items must be reintroduced into the same stream of items being delivered by the source. This reintroduction negatively affects item quality and production line efficiencies.
Horizontal accumulators do exist that operate on the FIFO principle, i.e., first in first out. However, these systems carry with them the disadvantages of breakage or damage caused by production line back pressure or less than acceptable production efficiencies in that production line back pressure results in locking or wedging of the accumulated items which in turn results in lower production line efficiencies. In addition, many horizontal accumulators that operate on the FIFO principle demand that the accumulated item be mechanically pushed from one portion of the conveying means to another portion of the conveying means. This mechanical pushing results in lower production line efficiencies when changing direction of movement from one direction to another, in that the probability of jamming or falling is increased. Many horizontal accumulators, both FIFO and LIFO, have great difficulty in maintaining the items in the same orientation as delivered by the source, e.g., labels on one side, pour spout at top, handle leading, etc. This fact negatively affects production line efficiencies.